The problem with Sedevacantism is that it's something positive. It's a positive declaration or choice. So once you set up that "Sedevacantist" chapel, it's hard to not constantly obsess about that one issue. After all, it's central to your chapel's identity!
Say I started a "European Traditional Catholic chapel" tomorrow. Wouldn't you expect there to be something different about that chapel, compared with your plain vanilla "Traditional Catholic chapel"? Of course you would. And you'd be right! The sermons would probably talk about Europe's role in Divine Providence more than most chapels, I'm sure all the saint statues and pictures would be of European saints, the parishioners would probably be above-average against immigration, there would probably be a few neo-nazis in the parish, and so forth. Long story short, if we didn't do something different at that chapel, we would be kind of silly to be so specific on our chapel's signage.
That's why I have to laugh about things like "Sedevacantist singles".
Is that where you throw darts at a picture of the current "antipope" with the girl you're courting, instead of going to the bowling alley? If the "sedevacantist" courting experience isn't significantly different than that of a regular non-sedevacantist "Traditional Catholic", then why be so strangely specific?
As an interesting corollary, this applies to "Traditional Catholic" as well.
Every day, I am faced with that adjective "Traditional" which reminds me that I reject the heresy of Modernism (as well as other modern errors like Freemasonry, Communism, Feminism), I value Tradition as much as I value Scripture. I am also reminded of the truth that the Catholic Faith is inherently Traditional, as well as the fact that there is a Crisis in the Church going on right now, and has been in progress for the last 46 years. It also reminds me that if we are in crisis and in a state of war, there's no room for the lukewarm. We must be soldiers for Christ like never before.
So yes, Traditional Catholics "Catholic" differently than regular (conciliar) Catholics. So the adjective is called for, and welcome.
How's that for an answer to the oft-posed, "Why can't we just call ourselves Catholic" question!